This invention relates to the field of shoes, and in particular, spring-cushioned shoes.
In most running, walking, and jumping activities, the return force resulting from foot strikes causes great shock to the body. The stress from repeated foot strikes places great stress on joints and bones, and can cause injuries to the lower back and the rotating joints of the legs.
To minimize injury to the body resulting from repeated foot strikes, and also to improve athletic performance, shoe engineers have designed various spring-cushioned shoes. The springs in spring-cushioned shoes are designed to reduce shock to the body during a foot strike, and also to recover and return impact energy to the user. One type of spring-cushioned shoe is described in U.S. Pat. No. 6,282,814 to Krafsur et al., which is incorporated herein by reference. Two other types of spring-cushioned shoes are described in U.S. Pat. No. 5,743,028 to Lombardino, and U.S. Pat. No. 4,815,221 to Diaz. The Lombardino ""028 patent discloses a plurality of vertical compression springs located in the heel area of a running shoe. The springs of the ""028 patent are housed in a hermetically sealed unit filled with a pressurized gas which in combination with the springs provides a shock absorption and energy return system. The Diaz ""221 patent discloses an energy control system placed within a cavity in the sole of a shoe. The energy control system includes a spring plate with a plurality of spring projections distributed over the surface of the plate for propulsion and shock absorption.
In the spring-cushioned shoe designs of the patents described above, the springs are sealed within vacuities formed in the soles of the shoe. When the springs are sealed within a vacuity, the air within the vacuity is an integral part of the spring system. During a foot strike, air sealed within the vacuities behaves according to the ideal gas law, PV=nRT, which states that the pressure of the air within the cavity, at a substantially constant temperature, varies inversely with the volume as the cavity is compressed. During a foot strike, therefore, the air exerts a return force as the volume of the cavity decreases. This return force exerted by the air interferes with the predictable return force exerted by the spring in response to a foot strike.
Thus, while trapped air in a shoe sole is thought to be desirable because the air provides cushioning and return force, in spring-cushioned shoes, the air interferes with the predictable operation of the spring.
Accordingly, it is an object of the invention to provide a fluid flow system as a part of a spring-cushioned shoe sole assembly that will reduce the spring-like reaction force of the fluid within a vacuity that contains a spring or springs.
A second object of the invention is to provide a spring-cushioned shoe sole assembly that returns, by way of the spring force, a substantial portion of the energy stored in the springs during the initial compression cycle of the heel or ball area of the foot.
In one aspect, the invention features a shoe that includes a shoe sole which defines a vacuity, a spring disposed within the vacuity, and a fluid passageway in fluid communication with the vacuity. The passageway is configured to allow evacuation of fluid from the vacuity upon a reduction in the volume of the vacuity.
Embodiments of this aspect of the invention may include one or more of the following features. The vacuity can be disposed within the heel region of the shoe sole, and the spring can be mounted within the vacuity between a pair of vertically opposed plates, disposed on upper and lower ends of the vacuity.
The sole can define a second vacuity, e.g., in the ball region, that may or may not include a spring, connected to the first vacuity by the fluid passageway. The two vacuities and the fluid passageway can be hermetically sealed from the exterior of the shoe, trapping fluid, such as ambient air, inside the vacuities. Trapped air can be sealed at atmospheric pressure, or at less than atmospheric pressure.
The fluid passageway may also include a channel that connects the vacuity to the exterior of the shoe, allowing evacuation of fluid to the exterior of the shoe upon reduction in volume of the vacuity.
The shoe sole may include an inner sole, a mid-sole, and an outer sole, where the mid-sole defines the vacuity. The mid-sole can be formed entirely from a compressible foamed polymeric material, or from, e.g., a foamed polymeric material and a flexible plastic material, where the flexible plastic material defines at least a portion of a wall of the vacuity. The spring can be, e.g., a crest-to-crest multi-turn wave spring.
In another aspect, the invention features a shoe sole assembly. The sole assembly includes a compressible material defining a vacuity, a spring disposed within the vacuity, and a fluid passageway in fluid communication with the vacuity. The passageway is configured to allow evacuation of fluid from the vacuity upon compression of the vacuity.
In another aspect, the invention features a method of manufacturing a spring-cushioned shoe sole assembly. The method includes: (a) forming at least a portion of the sole assembly from a compressible material, where the portion defines a vacuity; (b) disposing a spring within the vacuity; and (c) forming a fluid passageway in fluid communication with the vacuity, the passageway allowing fluid to escape from the vacuity upon compression of the vacuity.
As used herein, xe2x80x9cfluidxe2x80x9d means a substance that flows, such as a gas or a liquid. Ambient air is a fluid.
A xe2x80x9cspringxe2x80x9d is a resilient mechanical device that recovers its original shape when released after being distorted. A xe2x80x9ccompression springxe2x80x9d is a spring that is loaded (i.e., distorted) by compression. Types of compression springs include, for example: wave springs, such as nested wave springs, interlaced wave springs, and crest-to-crest wave springs (with or without shim ends); disc springs; Belleville springs; compound Belleville springs; spiral springs; and helical springs.
A xe2x80x9cmulti-turn springxe2x80x9d is a spring having multiple xe2x80x9cturns,xe2x80x9d where a turn is a revolution of the spring.
The details of several embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.